A typical ballast system for a gaseous discharge lamp comprises a ballast reactance, including a reactor coil in circuit with the lamp, for supplying energy to the lamp after the fill gas within the lamp has been initially ionized. This energy promotes glow-to-arc transition and subsequent arc operation. For effecting initial ionization of the fill gas, a starting aid, or ignitor, is provided for developing a high voltage pulse that is applied to the lamp when initiating lamp operation. In the case of a 70 watt high-pressure sodium lamp energized from a 120 volt, 60 Hz line, this high voltage pulse typically has a peak available value of 2500-4000 volts and a width of 1.5 to 15 microseconds at 2250 volts. The pulse should be within .+-.10 degrees of the peak of the sinusoidal line voltage. Without a starting aid, the typical 70 watt high-pressure sodium lamp will not initiate operation when the above line voltage is applied to the lamp.
The most common type starting aid utilizes a tap on the reactance coil of the ballast. A typical starting aid circuit that employs this approach is illustrated in U.S. Pat. Nos. 3,917,976 and 3,963,958 - Nuckolls, assigned to the assignee of the present invention. One disadvantage of relying upon a tap on the reactance coil is that it is expensive to manufacture a reactor coil that includes such a tap. Another disadvantage is that certain types of ballast, such as the pot-core ballast, do not readily lend themselves to the inclusion of a tap of the type here required, i.e., one to which a high voltage pulse is applied and which requires high voltage insulation to maintain the required dielectric strength. In the pot-core type ballast, grounded core structure completely envelopes the reactor coil, and this leads to difficulties and expenses in providing for a properly insulated tap.
Another type of starting aid is the so-called "remote" starting aid, which is sometimes utilized when the ballast reactor is far removed from the lamp. These starting aids contain high frequency transformers separate from the ballast reactor and in series with the lamp. Because these separate high frequency transformers are relatively expensive, this type of starting aid is typically considerably more expensive than the conventional tapped reactor type starting aid.